Lynch Syndrome I

A number sign (#) is used with this entry because Lynch syndrome I, also known as hereditary nonpolyposis colorectal cancer (HNPCC), is caused by heterozygous mutations in mismatch repair genes (MMR). HNPCC1 refers to the disorder caused by mutations in the MSH2 gene (609309).

Hereditary nonpolyposis colorectal cancer (HNPCC) is subdivided into (1) Lynch syndrome I, or site-specific colonic cancer, and (2) Lynch syndrome II, or extracolonic cancer, particularly carcinoma of the stomach, endometrium (see 608089), biliary and pancreatic system, and urinary tract (Lynch and Lynch, 1979; Lynch et al., 1985; Mecklin and Jarvinen, 1991). HNPCC disorders show a proclivity to early onset, predominant proximal location of colon cancer, a dominant pattern of inheritance, an excess of multiple primary cancers, and significantly improved survival when compared stage for stage with the American College of Surgeons Audit Series.

Lynch et al. (1991) estimated that hereditary nonpolyposis colorectal cancer accounts for about 4 to 6% of colorectal cancer. The minimum criterion of HNPCC is that colorectal carcinoma is diagnosed and histologically verified in at least 3 relatives belonging to 2 or more successive generations. Moreover, the age of onset should be less than 50 years in at least 1 patient.

The Muir-Torre syndrome (MRTES; 158320) is a form of Lynch syndrome II associated with sebaceous skin tumors.

Genetic Heterogeneity of HNPCC

HNPCC is a genetically heterogeneous disease. See also HNPCC2 (609310), caused by mutation in the MLH1 gene (120436); HNPCC4 (614337), caused by mutation in the PMS2 gene (600259); HNPCC5 (614350), caused by mutation in the MSH6 gene (600678); HNPCC6 (614331), caused by mutation in the TGFBR2 gene (190182); HNPCC7 (614385), caused by mutation in the MLH3 gene (604395). HNPCC8 (613244) results from epigenetic silencing of MSH2 caused by deletion of 3-prime exons of the EPCAM gene (185535) and intergenic regions directly upstream of the MSH2 gene.

Since defects in the MSH2 gene may account for as many as 60% of HNPCC cases, and defects in the MLH1 gene may play a role in up to 30%, defects in these 2 genes likely account for the vast majority of HNPCC cases.

Lynch Syndrome I

From findings in the Danish HNPCC Register, Myrhoj et al. (1997) concluded that colorectal cancer in HNPCC behaves differently from colorectal cancer in general. The mean age at diagnosis of primary CRC was 41 years as compared with 70 years for all Danish CRC. In 68%, the colon cancer was located proximal to the splenic flexure as compared with 49% in Danish CRC in general; the numbers for rectal location were 20% for HNPCC as compared with the general experience of 43%. In 7% of HNPCC, more than 1 colorectal cancer was found at the first operation, versus 1% in the general group. Metastatic tendency was less than in sporadic CRC and survival was better.

Lynch and de la Chapelle (1999) provided an extensive review of clinical features, pathology, molecular genetics, surveillance, and management in HNPCC. They emphasized the importance of ascertaining cancer of all anatomic sites as well as noncancer phenotypic stigmata in assessing a family cancer history to allow definition of the specific CRC syndrome concerned.

Parc et al. (2003) analyzed the age at onset and location of each cancer that had affected a series of 348 patients with HNPCC who had mutation in either the MSH2 or MLH1 gene. Tumor histories of these patients were remarkably similar. Ages at first tumor were not correlated within families. Tumors that developed before 30 years of age were all located in the colon or rectum. Cancers developed before 25 years of age in 5% of patients. Colorectal cancer risks were comparable in males and females but delayed in females by 5 to 10 years. Colorectal cancer was the first manifestation of the disease in 89% of affected males but in only 66% of affected females. Endometrial cancer was the first manifestation in 26% of affected females. Based on these findings, Parc et al. (2003) suggested the following: patients with colorectal or endometrial cancer less than 50 years of age should be invited for screening for MSH2 and MLH1 mutations; surveillance of gene carriers should be initiated in early adulthood (i.e., age 18 years), and should not be delayed by the age at onset of the index case; and up to the age of 30 years, surveillance should focus on the colorectum for both sexes.

Bellacosa et al. (1996) reviewed genetic counseling aspects of HNPCC against the background of the clinical and molecular genetics.

Barrow et al. (2008) analyzed the cumulative lifetime incidence of developing colorectal cancer by age 70 years in 121 families with genetically confirmed Lynch syndrome. Fifty-one families had MLH1 mutations, 59 had MSH2 mutations, and 11 had MSH6 mutations. The first analysis corrected for ascertainment bias by allocating mutation carrier status to a proportion of unaffected, untested family members. In this first analysis, mutation carriers had an overall 50.4% cumulative risk of developing colorectal cancer by age 70 years (54.3% in men and 46.3% in women). The risk to men with MLH1, MSH2, and MSH6 mutations was 57.9%, 53.6%, and 36.2%, respectively, whereas for women it was 50.2%, 47.7%, and 18.3%, respectively. Women mutation carriers overall had a cumulative 28.2% incidence of endometrial cancer to age 70 years. The overall risk for colorectal cancer increased to 74.5% (78.4% in men and 70.8% in women) in a second analysis that included only proven mutation carriers. In the second analysis, the cumulative risk for development of colorectal cancer by age 70 years in men was 75.4%, 83.1%, and 55.6%, for MLH1, MSH2, and MSH6 mutations, respectively. Women had a cumulative risk of 76.9%, 72.6%, and 31.4% for MLH1, MSH2, and MSH6 mutations, respectively. Cumulative 5- and 10-year survival following colorectal cancer in all mutation carriers was 56.2% and 50.0%, respectively. There were no difference in 5-year survival by mutation or gender.

Lynch Syndrome II

Lynch et al. (1966) and Lynch and Krush (1967) suggested the existence of a syndrome, which they called the 'cancer-family syndrome,' characterized by autosomal dominant inheritance of endometrial carcinoma and adenocarcinoma of the colon, as well as multiple primary malignant neoplasms. Lynch and Lynch (1979) pointed out that cancer of the right colon is particularly characteristic of the cancer-family syndrome. Features of cancers with a genetic origin include early age of onset, bilaterality or multifocality, multiplicity of primary cancers, and, of course, familiality. Lynch et al. (1973) suggested that among families with breast cancer some have an excess of ovarian cancer, others are prone to sarcoma, brain tumors and leukemia, whereas yet others have associated gastrointestinal cancer.

Warthin's original description of 'Family G' (Warthin, 1913) showed an excess of gastric cancer. A decline in incidence of gastric carcinoma and an increase in colonic cancer was found to have a parallel in Family G on update by Lynch and Krush (1971).

Lynch et al. (1981) reported a family with a high incidence of cancer. The proband developed colon cancer at age 39 years. Eight female relatives, including his mother, her twin sister, and their daughters had ovarian carcinoma. In the proband's sibship, 6 of 8 had cancer of differing anatomic sites. The susceptibility to ovarian carcinoma appeared to have been transmitted through the men; 1 was cancer-free while 2 had cancer. The phenotype was consistent with Lynch syndrome.

Cristofaro et al. (1987) and Guanti et al. (1990) described an extensively affected Italian family with the characteristic features of the Lynch cancer family syndrome II: early age of onset of tumors, increased frequency of adenocarcinomas of the colon, mainly with proximal location, and high occurrence of gastric, endometrial, and multiple primary malignancies. Unique pathologic findings included chronic atrophic gastritis and an excess of macrophages in association with atrophy of crypts in the colonic mucosa. Abusamra et al. (1987) described a family in which 8 cancers (6 colonic and 2 endometrial) occurred in 7 members of 3 generations. The colonic cancer was diagnosed in 5 of the 6 affected patients at an unusually young age, had a predilection for the proximal colon, and was of the mucinous type in 4 patients. No polyposis was found.

In a retrospective U.S. population-based study, Kastrinos et al. (2009) found 31 cases of pancreatic cancer among 81 families with MSH2 mutations, which corresponded to a hazard ratio of 10.9 in MSH2 mutation carriers compared to the general U.S. population. The authors concluded that pancreatic cancer is a component of HNPCC.

Patients with Lynch syndrome are at increased risk of developing extracolonic cancers, including endometrial, ovarian, small bowel, biliary tract, urothelial, and bladder cancer (summary by van der Post et al., 2010).

Haraldsdottir et al. (2014) analyzed the incidence of prostate cancer in males with Lynch syndrome. The authors included all males diagnosed with Lynch syndrome from June 1998 to June 2012 at the Ohio State University, and obtained baseline information, including cancer history. Of the 188 males identified with Lynch syndrome, 11 were diagnosed with prostate cancer during the study period. The ratio of observed to expected numbers of prostate cancer cases resulted in a standardized rate ratio of 4.87 (95% confidence interval: 2.43-8.71). Impaired mismatch repair expression and microsatellite instability were seen in 1 of 2 prostate cancer specimens available for testing. Haraldsdottir et al. (2014) concluded that males with Lynch syndrome had a nearly 5-fold increased risk of developing prostate cancer but did not appear to have earlier onset or a more aggressive phenotype.

Several guideline protocols have been developed in order to identify families with inherited colorectal cancer and/or Lynch syndrome. The Amsterdam (AMSI) criteria (Vasen et al., 1991) were initially coined to identify families with colorectal cancer. The finding of extracolonic cancers, especially endometrial cancer, in Lynch syndrome prompted introduction of the revised Amsterdam criteria (AMSII) (Vasen et al., 1999). The Bethesda guidelines included testing for tumor marker microsatellite instability (MSI) (Rodriguez-Bigas et al., 1997), and the revised Bethesda criteria (BII) (Umar et al., 2004) specified all cancers known at the time to be associated with the syndrome. Prostate cancer has also been shown to be part of the syndrome (summary by Sjursen et al., 2010).

Not all families fulfilling the clinical criteria for HNPCC (or Lynch syndrome) have an identifiable deleterious mutation in the MMR genes, and conversely, families not fulfilling the criteria have been found to harbor MMR mutations. Sjursen et al. (2010) reported sensitivity analysis for diagnostic criteria for Lynch syndrome among 129 families with proven mutations in the MMR genes. The original Amsterdam clinical criteria were met by 38%, 12%, 78% and 25% of families with mutations in MSH2, MSH6, MLH1 and PMS2, respectively. Corresponding numbers for the revised Amsterdam criteria were 62%, 48%, 87% and 38%. The Bethesda II criteria had low sensitivity for identifying MSH6 or PMS2 mutations. Sjursen et al. (2010) concluded that the Amsterdam criteria and each of the subgroups of the Bethesda II criteria were inadequate for identifying MSH6 mutation-carrying kindreds, implying that MSH6 mutations may be more common than currently assumed.

Cross et al. (2013) determined the availability of Lynch syndrome screening criteria and actual Lynch syndrome screening in the medical records of 1,188 patients diagnosed with metastatic colorectal cancer between 2004 and 2009 at 7 institutions in the Cancer Research Network. Cross et al. (2013) found infrequent use of Lynch syndrome screening (41 of 1,188). Family history was available for 937 of the 1,188 patients (79%). There was sufficient information to assess Lynch syndrome risk using family history-based criteria in 719 of the 937 patients (77%) with family history documentation. In 391 individuals with a family history of a Lynch syndrome-associated cancer, 107 (27%) could not be evaluated due to missing information such as age of cancer onset. Eleven percent of patients who met the Bethesda criteria and 25% of individuals who met the Amsterdam II criteria were screened for Lynch syndrome. Cross et al. (2013) concluded that the information required for Lynch syndrome screening decisions is routinely collected but seldom used.

HNPCC occurs mostly in the proximal colon. Rijcken et al. (2002) investigated whether this preponderance was due to a tendency for adenomas to develop more proximally and/or whether transformation rates were higher in proximal adenomas. One hundred HNPCC adenomas were compared with 156 sporadic adenomas; although both groups exhibited dysplasia, this was significantly more severe in proximal HNPCC adenomas 5 mm or more in size. Small HNPCC adenomas were no different from sporadic adenomas, except for their proximal location compared with sporadic adenomas. Thus, progression to high grade dysplasia was more common in proximal than distal HNPCC adenomas, indicating a faster transformation rate from early adenoma to cancer in the proximal colon.

Peltomaki et al. (1992) performed linkage studies in 9 Finnish families, demonstrating that HNPCC is not linked to the MCC (mutated in colon cancer; 159350)/APC (611731) region on 5q21; combined maximum lod score = -22.57 at a recombination fraction of 0.00. The report demonstrated the feasibility of studying DNA not only from blood samples from living family members but also from formaldehyde-fixed archival pathology specimens from deceased individuals.

One problem in establishing proof of a genetic component in colon cancer was that such cancers are so common that it was difficult to rule out chance clustering and other nonhereditary factors. Moreover, the environment, notably diet, has been shown to play a substantial role in colon cancer; members of families are likely to share similar environments, thus complicating definitive analysis. Peltomaki et al. (1993) and Aaltonen et al. (1993) searched for evidence of a genetic component through linkage analysis. In studies of 2 large kindreds, many individuals who had colon cancer with or without endometrial cancer (608089) were found to show linkage to an anonymous microsatellite marker on chromosome 2, D2S123, which means that a gene is in the region of 2p16-p15. The residence of the 2 kindreds on 2 different continents made an environmental explanation unlikely.

Aaltonen et al. (1993) studied an additional 14 smaller kindreds. Linkage could be excluded in 3 families by lod scores less than -2.0, whereas the remaining 11 smaller families displayed varying degrees of positive and negative lod scores, suggesting genetic heterogeneity. Aaltonen et al. (1993) found, furthermore, no loss of heterozygosity for the D2S123 or other chromosome 2 markers in either familial or sporadic cases of FCC and the incidence of mutations in KRAS, P53, and APC was similar in the 2 groups of tumors. They found, however, that most of the familial cancers had widespread alteration in short repeated DNA sequences, (CA)n dinucleotide repeat fragments, suggesting that numerous replication errors had occurred in the sequences during tumor development. In 13% of sporadic cancers, identical abnormalities were found and these cancers shared biologic properties with the familial cases, namely, location on the right side of the colon and preservation of diploidy or near-diploidy. Aaltonen et al. (1993) proposed that these findings reflect the existence on chromosome 2 of a gene which is neither an oncogene nor a tumor suppressor gene but rather a gene leading to genomic instability.

Using a panel of microsatellite polymorphisms in the vicinity of D2S123, Green et al. (1994) tested 7 Canadian HNPCC families. Whereas 1 family was clearly linked to the COCA1 locus (lod = 4.21) and a second family was probably linked (lod = 0.92), linkage was excluded in 3 families. In the remaining 2 families, the data were inconclusive. In the definitely linked family, individuals with cancer of the endometrium or ureter shared a common haplotype with 12 family members with colorectal cancer. This supported the suspected association between these extracolonic neoplasms and the HNPCC syndrome. In addition, 5 of the 6 persons with adenomatous polyps, but no colorectal cancer, had the same haplotype as the affected persons, while the sixth carried a recombination. One individual with colorectal cancer carried a recombination that placed the COCA1 locus telomeric to D2S123.

Thibodeau et al. (1993) examined colorectal tumor DNA for somatic instability at (CA)n repeats on 5q, 15q, 17p, and 18q. Differences between tumor and normal DNA were detected in 25 of the 90 tumors studied. The instability appeared as either a substantial change in repeat length (often heterogeneous in nature) or a minor change (typically 2 bp). There was a significant correlation between microsatellite instability and location of the tumor in the proximal colon, i.e., the right colon, and with increased patient survival; instability was correlated inversely with loss of heterozygosity for 5q, 17p, and 18q.

Ionov et al. (1993) found that 12% of colorectal carcinomas (CRCs) carry somatic deletions in poly(dA/dT) sequences and other simple repeats. They estimated that cells from these tumors can carry more than 100,000 such mutations. They concluded that these mutations reflect a previously undescribed form of carcinogenesis in the colon mediated by a mutation in a DNA replication factor resulting in reduced fidelity for replication or repair--a 'mutator mutation.'

The subset of sporadic colorectal tumors and most tumors developing in HNPCC patients, containing alterations in microsatellite sequences, are thought to manifest replication errors and are referred to as RER(+) for 'replication errors.' Using genetic criteria, Parsons et al. (1993) demonstrated that the mutation rate of (CA)n repeats in RER(+) tumor cells is at least 100-fold that in RER(-) tumor cells and affects extrachromosomal as well as endogenous genomic sequences. Moreover, using in vitro assays, they showed that the mutability of RER(+) cells is associated with a profound defect in strand-specific mismatch repair. This deficiency was observed with microsatellite heteroduplexes as well as with heteroduplexes containing single base-base mismatches and affected an early step in the repair pathway. Thus, a true mutator phenotype exists in a subset of human tumors. The responsible defect is likely to cause transitions and transversions in addition to microsatellite alterations.

Fishel et al. (1993) studied human homologs of the mismatch repair system in Escherichia coli referred to as the MutHLS pathway. The pathway promotes a long patch (approximately 2 kb) excision repair reaction that is dependent on the products of the MutH, MutL, MutS, and MutU genes. Genetic analysis suggested that Saccharomyces cerevisiae has a mismatch repair system similar to the bacterial MutHLS system. The S. cerevisiae pathway has a MutS homolog, MSH2. In both bacteria and S. cerevisiae, mismatch repair plays a role in maintaining the genetic stability of DNA. In S. cerevisiae, Msh2 mutants exhibit increased rates of expansion and contraction of dinucleotide repeat sequences. Fishel et al. (1993) cloned and characterized a human MutS homolog, MSH2, which maps to chromosome 2p22-p21. They identified a T-to-C transition in the -6 position of a splice acceptor site in sporadic colon tumors and as a constitutional change in affected members of 2 small families with HNPCC. Fishel et al. (1993) were prompted to study the human homolog MSH2 following the report by Aaltonen et al. (1993) that the mutation in nonpolyposis colon cancer that maps to 2p behaves like a defect in DNA repair of the MutHLS type, which they had previously been studying.

Leach et al. (1993) used chromosome microdissection to obtain highly polymorphic markers from 2p16. These and other markers were ordered in a panel of somatic cell hybrids and used to define a 0.8-Mb interval containing the locus for HNPCC. Candidate genes were mapped with respect to this locus, and one gene, MSH2, was found to lie within the 0.8-Mb interval. (Disruption of the MutL and MutS mismatch repair (MMR) genes produces microsatellite instability in bacteria and yeast (Levinson and Gutman, 1987; Strand et al., 1993).) Using the sequence of cDNA clones of the gene, they demonstrated the existence of germline mutations that substantially altered the predicted gene product and cosegregated with disease in the HNPCC kindreds. Furthermore, Leach et al. (1993) succeeded in identifying specific germline mutations in each of the 2 kindreds that originally established linkage to chromosome 2 (609309.0001; 609309.0002) (Peltomaki et al., 1993). It is noteworthy that both the candidate gene approach and positional cloning, the 2 main methods of map-based cloning, were used in identifying the MSH2 gene.

Liu et al. (1996) evaluated tumors from 74 HNPCC kindreds for genomic instability characteristic of an mismatch repair gene deficiency and found such instability in 68 (92%) of the kindreds. The entire coding regions of the 5 known human MMR genes were evaluated in 48 kindreds with instability, and mutations were identified in 70%: mutations in the MSH2 gene in 15 (31%), in the MLH1 gene in 16 (33%), in the PMS1 gene in 1 (2%), in the PMS2 gene, in 2 (4%), and in the GTBP gene (MSH6) in none. The study was interpreted as demonstrating that a combination of techniques can be used for genetic diagnosis of tumor susceptibility in most HNPCC kindreds and laid the foundation for genetic testing of this relatively common disease. Plummer and Casey (1996) pointed out that one of challenges of genetic testing for HNPCC is the development of a standard set of protocols that can be applied to the analysis of multiple candidate genes. In families meeting the strict International Collaborative Group (ICG) definition of HNPCC, the youngest living affected family member should initially be screened for germline mutations in the 2 most commonly mutated MMR genes (MSH2 and MLH1). In individuals who do not meet the strict ICG definition but appear to have a familial predisposition to colon cancer reminiscent of HNPCC, Liu et al. (1996) proposed that mutation analysis be performed only if RER indicating genomic instability characteristic of a MMR deficiency is identified in the tumor of an affected individual. They noted that difficulty is that it is often impossible to obtain blood samples from living affected relatives. In fact, in the study by Liu et al. (1996), blood samples for germline analysis could be obtained from only 48 of the 68 kindreds showing the RER phenotype.

Pensotti et al. (1997) screened 14 Italian families affected with HNPCC for germline mutations of the MSH2, MLH1, and GTBP genes. DNA alterations were observed in 6 of the families, involving MSH2 or MLH1. No mutations were detected in the G/T binding protein (GTBP; 600678). (GTBP codes for a 160-kD protein that interacts with the product of MSH2. Although mutations of the GTBP gene had been observed in colon cancer cell lines, germline alterations had not been reported in HNPCC patients.) A finding of note by Pensotti et al. (1997) was that the kindreds with demonstrated mutations had a mean age of colorectal cancer onset of 43 years versus an average age of 53 years for the families without mutations.

Fearon (1997) reviewed more than 20 different hereditary cancer syndromes that had been defined and attributed to specific germline mutations in various inherited cancer genes. In a useful illustration, he diagrammed the roles of allelic variation ('one gene - different syndromes') and genetic heterogeneity ('different genes - one syndrome') in inherited cancer syndromes. The example he used of the latter was HNPCC resulting from mutations in various MMR genes.

To evaluate the feasibility of molecular screening for HNPCC, Aaltonen et al. (1998) prospectively screened tumor specimens obtained from 509 consecutive Finnish patients with colorectal adenocarcinomas for DNA replication errors, which are characteristic of hereditary colorectal cancers. These replication errors were detected through microsatellite-marker analyses of tumor DNA. DNA from normal tissue from the patients with replication errors were screened for germline mutations in MLH1 and MSH2. Among the 509 patients, 63 (12%) had replication errors. Specimens of normal tissue from 10 of these 63 patients had a germline mutation of MLH1 or MSH2. Of these 10 patients (2% of the 509 patients), 9 had a first-degree relative with endometrial or colorectal cancer, 7 were under 50 years of age, and 4 had had colorectal or endometrial cancer previously. Aaltonen et al. (1998) recommended testing for replication errors in all patients with colorectal cancer who meet one or more of the following criteria: a family history of colorectal or endometrial cancer, an age of less than 50 years, and a history of multiple colorectal or endometrial cancers. Patients found to have replication errors should undergo further analysis for germline mutations in DNA mismatch repair genes.

Lynch and Smyrk (1998) noted that several groups have proposed less restrictive criteria, including the Bethesda criteria (Rodriguez-Bigas et al., 1997) and the Japanese criteria (Nakahara et al., 1997). While applauding the trend toward less restrictive criteria, they doubted that in actual practice clinicians will find any algorithm particularly useful in deciding on which patients to test.

Wijnen et al. (1998) assessed the prevalence of MSH2 and MLH1 mutations in families suspected of having hereditary nonpolyposis colorectal cancer and evaluated whether clinical findings can predict the outcome of genetic testing. They studied 184 kindreds; mutations of one or the other gene were found in 47 (26%). Clinical factors associated with these mutations were early age at diagnosis of colorectal cancer, the occurrence in the kindred of endometrial cancer or tumors of the small intestine, a higher number of family members with colorectal or endometrial cancer, the presence of multiple colorectal cancers or both colorectal and endometrial cancers in a single family member, and fulfillment of the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer (at least 3 family members in 2 or more successive generations must have colorectal cancer, 1 of whom is a first-degree relative of the other 2; cancer must be diagnosed before the age of 50 in at least 1 family member; and familial adenomatous polyposis must be ruled out). Multivariate analysis showed that a younger age at diagnosis of colorectal cancer, fulfillment of the Amsterdam criteria, and the presence of endometrial cancer in the kindred were independent predictors of germline mutations of MSH2 or MLH1. Wijnen et al. (1998) used these results to devise a logistic model for estimating the likelihood of a mutation in MSH2 and MLH1.

Bapat et al. (1999) screened the MSH2 and MLH1 genes for germline mutations in 33 cases/families who met Mount Sinai criteria for familial colorectal cancer, only 14 of whom met the more stringent Amsterdam criteria. Mutations were identified in 8 of 14 Amsterdam criteria families and 5 of 19 remaining, 3 of whom had features of the Muir-Torre syndrome (158320). A high level of microsatellite instability was detected in 16 of 18 colorectal cancers from individuals with MSH2 and MLH1 mutations and infrequently (1 of 21) in colorectal cancers from individuals without detectable mutations. Families with germline mutations had individuals affected at younger ages and with multiple tumors. The authors suggested that colorectal cancer family criteria need revision to more accurately identify those who would benefit from MSH2 and MLH1 mutation analysis.

In studies of a cohort of 22 patients with HNPCC and evidence of MMR deficiency in their tumors, Yan et al. (2000) demonstrated the value of the conversion approach to mutation analysis. This approach overcomes the problem of mutations in one copy of a chromosome pair being obscured by the normal sequence present on the other copy by converting the human chromosome complement to a haploid state through fusion to a recipient cell line. Using conventional techniques, Yan et al. (2000) were unable to identify MMR mutations in 10 of the 22 patients. Using conversion technology, they identified disease-causing alterations in all 22 patients. Three of the cases were due to large deletions of the MSH2 gene. Only the normal sequences inherited from the unaffected parent were amplified from the diploid cells of these patients, explaining the failure of conventional approaches based on PCR to reveal the defects. In 3 other cases, no MLH1 transcript was generated from 1 allele, although the sequences of all exons and intron-exon borders from this allele were normal. Presumably, mutations deep within introns or in the promoter of the MLH1 gene were responsible. Four other cases were due to point mutations in the MSH2 gene. These mutations were not detected in analogous templates from diploid cells because the signals from the mutant allele were weaker than those from the normal allele. Such asymmetry is a common problem for both manual and automated sequencing methods, but was eliminated through conversion because only 1 sequence can be present in each nucleotide position. One of the families studied by Yan et al. (2000) was the large colon cancer family, family G, reported in the historic paper of Warthin (1913). Affected members of this family were found to have a 24-bp insertion between codons 215 and 216 (609309.0013).

Endometrial cancer is the most common extracolonic neoplasm in HNPCC and is the primary clinical manifestation of the syndrome in some families. The cumulative incidence of endometrial cancer among HNPCC mutation carriers is high, estimated to be between 22 and 43%. Millar et al. (1999) hypothesized that women with double primary cancers of the colorectum and endometrium are likely to be members of HNPCC families. To test this hypothesis, they examined alterations of 2 MMR genes, MSH2 and MLH1, in 40 unrelated women affected with double primary cancers. In 7 of the 40 cases (18%), a mutation of 1 of the 2 MMR genes was found. Analysis of colorectal and/or endometrial tumors of mutation-negative probands found microsatellite instability in 7 of 20 cases. A strong family history suggestive of HNPCC was found in 6 of 7 mutation-positive probands.

Loukola et al. (1999) reported an evaluation of a logistic model based on family history data for the detection of HNPCC patients with germline mutations. A series of 509 kindreds with a proband with colorectal cancer were studied. Sixty-three probands (12%) were MSI-positive, 10 (2%) of whom had a germline mutation in MLH1 or MSH2. The results of this report were found to be in error and were corrected. In the erratum, the authors stated that the logistic model was able to detect 6 out of 10 (with first-degree pedigrees) and 8 out of 10 (with extensive pedigrees) mutation carriers. The authors also studied an additional 535 similar kindreds and concluded that statistical formulas are of limited value and that use of tools such as MSI screening is warranted.

Kraus et al. (1999) reported a germline mutation causing a frameshift due to a 1-bp deletion in the MSH2 gene in a male proband who developed a rectal adenoma at the age of 25 years and, 10 years later, an invasive right-sided colonic carcinoma. There was no family history of colon cancer, and analysis of the parents confirmed that this was a de novo mutation. Kraus et al. (1999) suggested that mutation screening of the MSH2 and MLH1 genes be performed in individuals with HNPCC-related tumors diagnosed before the age of 45 years even in the absence of a family history.

Syngal et al. (2000) classified 70 families with suspected hereditary colorectal cancer, excluding familial adenomatous polyposis, by several existing clinical criteria for HNPCC. Of the 70 families, 28 fulfilled the Amsterdam criteria, 39 fulfilled the Modified Amsterdam criteria, 34 fulfilled the Amsterdam II criteria, and 56 fulfilled at least 1 of the 7 Bethesda Guidelines for the identification of HNPCC patients. The results of analysis of the mismatch repair genes MSH2 and MLH1 were available for a proband with colorectal neoplasia in each family. The sensitivity and specificity of the Amsterdam criteria were 61% and 67%; the sensitivity of the Modified Amsterdam and Amsterdam II criteria were 72% and 78%, respectively. Overall, the most sensitive criteria for identifying families with pathogenic mutations were the Bethesda criteria, with a sensitivity of 94%; however, the specificity was 25%. Use of the first 3 criteria of the Bethesda Guidelines only was associated with a sensitivity of 94% and a specificity of 49%. Syngal et al. (2000) concluded that the Amsterdam criteria for HNPCC were neither sufficiently sensitive nor specific for use as the sole criteria for determining which families should undergo testing for MSH2 and MLH1 mutations, and that the modified Amsterdam and Amsterdam II criteria still miss many families with mutations. They suggested that a streamlined version of the Bethesda Guidelines may be more specific and easier to use in clinical practice.

Peltomaki (2001) reviewed the genetics of HNPCC and, more generally, of cancer development driven by deficient DNA mismatch repair.

Cunningham et al. (2001) analyzed somatic and germline mutations in the DNA mismatch repair genes to clarify the prevalence and mechanism of inactivation in colorectal cancer. They examined 257 unselected patients referred for colorectal cancer resection for evidence of defective DNA MMR. MMR status was assessed by the testing of tumors for the presence or absence of MLH1, MSH2, and MSH6 protein expression and for microsatellite instability. Of the 257 patients, 51 (20%) had evidence of defective MMR, demonstrating high levels of MSI and an absence of either MLH1 (48 patients) or MSH2 (3 patients). All 3 patients lacking MSH2, as well as 1 patient lacking MLH1, also demonstrated an absence of MSH6. DNA sequence analysis of the 51 patients with defective MMR revealed 7 germline mutations: 4 in MLH1 (2 truncating, 2 missense) and 3 in MSH2 (all truncating). A detailed family history was available for 225 of the 257 patients. Of the 7 patients with germline mutations, only 3 had family histories consistent with HNPCC. Of the remaining patients who had tumors with defective MMR, 8 had somatic mutations in MLH1. In addition, hypermethylation of the MLH1 gene promoter was present in 37 (88%) of the 42 MLH1-negative cases available for study and in all tumors demonstrating a high level of MSI that showed loss of MLH1 expression but no detectable MLH1 mutations. The results suggested that, although defective DNA MMR occurs in approximately 20% of unselected patients presenting for colorectal cancer resection, hereditary colorectal cancer due to mutations in the MMR pathway account for only a small proportion of patients. Of the 257 patients, only 5 (1.9%) appeared to have unequivocal evidence of hereditary defects in MMR. The epigenetic (nonhereditary) mechanism of MLH1 promoter hypermethylation appears to be responsible for most of the remaining patients whose tumors are characterized by defective DNA MMR.

In hereditary nonpolyposis colorectal cancer, a large proportion of mutations detected in MSH2 are of the missense type; these may represent deleterious sequence changes or harmless polymorphisms. In order to determine whether such sequence changes could be interpreted as pathogenic, Cravo et al. (2002) investigated 10 Portuguese families with a history of colorectal cancer in whom a missense or splice site mutation in either MSH2 or MLH1 had been detected in the proband. In most families there was no definite evidence that the missense mutations or splice site mutation were causally associated with an increased risk of developing colorectal carcinoma. The authors suggested that such mutational events should be interpreted with great caution.

Germline PTEN (601728) mutations cause Cowden syndrome (158350) a hamartoma-tumor syndrome with an increased risk of breast, thyroid, and endometrial cancers. Somatic genetic and epigenetic inactivation of PTEN is involved in as high as 93% of sporadic endometrial carcinomas, irrespective of microsatellite status, and can occur in the earliest precancers. Endometrial carcinoma is the most frequent extracolonic cancer in patients with HNPCC. Zhou et al. (2002) obtained 41 endometrial carcinomas from 29 MLH1 or MSH2 mutation-positive HNPCC families and subjected them to PTEN expression and mutation analysis. Immunohistochemical analysis revealed 68% (28 of 41) of the HNPCC-related endometrial carcinomas with absent or weak PTEN expression. Mutation analysis of 20 aberrant PTEN-expressing tumors revealed that 17 (85%) harbored 18 somatic PTEN frameshift mutations. Ten mutations (56%) involved the 6(A) tracts in exon 7 or 8. The authors suggested that PTEN may play a significant pathogenic role in both HNPCC and sporadic endometrial carcinogenesis. They further concluded that somatic PTEN mutations, especially frameshift, are a consequence of profound MMR deficiency in HNPCC-related endometrial carcinomas.

Wagner et al. (2003) analyzed 59 clinically well-defined U.S. families with HNPCC for MSH2, MLH1, and MSH6 mutations. To maximize mutation detection, several different techniques were used. In 45 (92%) of the 49 Amsterdam-criteria-positive families and in 7 (70%) of the 10 Amsterdam-criteria-negative families, a mutation was detected in 1 of the 3 analyzed major MMR genes. Forty-nine mutations were in MHS2 or MLH1, and only 3 were in MSH6. A considerable proportion (27%) of mutations were genomic rearrangements (12 in MSH2 and 2 in MLH1). Notably, a 16-kb deletion encompassing exons 1-6 of MSH2 (609309.0018) was detected in 7 apparently unrelated families (12% of the first cohort), was identified in 2 unrelated families from a second cohort, and was subsequently proven to be a founder mutation. The 16-kb deletion encompassing exons 1-6 of the MSH2 gene was present in approximately 10% of the American families studied. Genealogic, molecular, and haplotype studies showed that this deletion represented a mutation that could be traced back to the 19th century. Lynch et al. (2004) reported that to date 61 of 566 family members of the 9 probands have been found to carry the 16-kb deletion. Three families have been genealogically shown to descend from a German immigrant family that settled in Pennsylvania in the early 1700s. Movements of branches of the extended family have been documented across the U.S. The 16-kb deletion was not found among 407 European and Australian families with HNPCC.

Watson et al. (2003) studied the change in distribution of carrier risk status resulting from molecular testing in 47 families with HNPCC and 75 families with hereditary breast-ovarian cancer. Carrier risk status changes from uncertainty to certainty (i.e., to carrier or to noncarrier) accounted for 89% of risk changes resulting from testing. These risk changes affect cancer prevention recommendations, most commonly reducing their burden. Watson et al. (2003) found that 60% of persons with a carrier risk status change were not themselves tested; their risk status changed because of a relative's test result. They noted that practices in use at the time did not ensure that untested family members were informed about changes in their carrier risk status resulting from mutation testing of their relatives.

Wang et al. (2002) described a modified multiplex PCR assay effective in detecting large deletions in either the MSH2 or MLH1 gene in HNPCC.

Taylor et al. (2003) demonstrated that genomic deletions in MSH2 or MLH1 are a frequent cause of HNPCC and that these deletions can be efficiently demonstrated by the multiplex ligation-dependent probe amplification (MLPA) assay.

Hampel et al. (2005) undertook an assessment of the frequency of mutations causing HNPCC, which they referred to as Lynch syndrome, in patients with colorectal cancer and examined strategies for molecular screening to identify patients with the syndrome. Of 1,066 patients enrolled in the study, 208 (19.5%) had microsatellite instability, and 23 of these patients had a mutation causing HNPCC (2.2%). In 5 the mutation was located in the MLH1 gene (120436), in 13 in MSH2 (609309), in 3 in MSH6 (600678), and in 1 in PMS2 (600259). Hampel et al. (2005) concluded that routine molecular screening of patients with colorectal adenocarcinoma for HNPCC identified mutations in patients and their family members who otherwise would not have been detected. These data suggested that the effectiveness of screening with immunohistochemical analysis of the MMR proteins would be similar to that of the more complex strategy of genotyping for microsatellite instability.

In a systematic search by Southern blot analysis in a cohort of 439 HNPCC families for genomic rearrangements in the main MMR genes, van der Klift et al. (2005) identified 48 genomic rearrangements that cause an inherited predisposition to colorectal cancer in 68 unrelated kindreds. MSH2 was involved in 29 of the 48 rearrangements, MLH1 in 13, MHS6 in 2, and PMS2 in 4. The vast majority were deletions, although 1 previously described large inversion, an intronic insertion, and a more complex rearrangement were also found. Most of the deletion breakpoints fell within repetitive sequences, mainly Alu repeats, in agreement with the differential distribution of deletions between the MSH2 and MLH1 genes: the higher number and density of Alu repeats in MSH2 corresponded with a higher incidence of genomic rearrangement at this disease locus when compared with other MMR genes. Long interspersed nuclear element (LINE) repeats, relatively abundant in MLH1, for example, did not seem to contribute to the genesis of the deletions, presumably because of their older evolutionary age and divergence among individual repeat units when compared with short interspersed nuclear element (SINE) repeats, including Alu repeats. Southern blot analysis of the introns and the genomic regions flanking the MMR genes allowed detection of 6 novel genomic rearrangements that left the coding region of the disease-causing gene intact. These rearrangements comprised 4 deletions upstream of the coding region of MSH2 (3 cases) and MSH6 (1 case), a 2-kb insertion in intron 7 of PMS2, and a small (459-bp) deletion in intron 13 of MLH1.

Rustgi (2007) reviewed the genetics of hereditary colon cancer, including APC.

Stella et al. (2007) analyzed the MSH2 gene in 4 probands from Italian HNPCC families and identified deletions in all 4; 2 carried a 32-kb deletion encompassing exons 1-6 (609309.0023). Haplotype analysis of the 2 families with the MSH2 exons 1-6 deletion suggested that it is probably a founder mutation. Analysis of 23 affected parent-child pairs in the 4 kindreds showed that median age at diagnosis was anticipated in the offspring by 12 years (p = 0.0001). The authors noted that skin cancers, including 4 keratoacanthomas, had been reported in 10 of the 19 affected members of family V+Va, and 1 patient from family C had a squamous cell acanthoma. Families V and Va, which had been previously described by Barana et al. (2004) (see Muir-Torre syndrome, 158320) and van der Klift et al. (2005) (family It1), respectively, were found to be branches of the same large Italian family described by Stella et al. (2007).

Tang et al. (2009) identified pathogenic mutations or deletions in the MLH1 or MSH2 gene in 61 (66%) of 93 Taiwanese families with HNPCC. Forty-two families had MLH1 mutations, including 13 with the R265C mutation (120436.0030) and 5 with a 3-bp deletion (1846delAAG; 120436.0018). Thirteen of the MLH1 mutations were novel; in addition, 6 large MLH1 deletions were also found.

Velho et al. (2010) screened 174 primary gastrointestinal cancers (48 hereditary and 126 sporadic forms) and 7 colorectal cancer cell lines for MLK3 (MAP3K11; 600050) mutations. MLK3 mutations were significantly associated with microsatellite instability (MSI) phenotype in primary tumors (p = 0.0005), occurring in 21% of the MSI carcinomas. Most MLK3 somatic mutations identified were of the missense type (62.5%), and more than 80% of them affected evolutionarily conserved residues. A predictive 3D model demonstrated that MLK3 missense mutations clustered in the kinase domain, but probably affected scaffold properties rather than kinase activity. MLK3 missense mutations showed transforming capacity in vitro, and cells expressing the mutant gene were able to develop locally invasive tumors when subcutaneously injected in nude mice. In primary tumors, MLK3 mutations occurred in KRAS (190070) and/or BRAF (164757) wildtype carcinomas, although not being mutually exclusive genetic events.

Modification of Cancer Risk

Bellido et al. (2013) evaluated the role of the TERT (187270) single-nucleotide polymorphism (SNP) rs2075786 as a cancer-risk modifier in Lynch syndrome, studying 255 and 675 MMR gene mutation carriers from Spain and the Netherlands, respectively. The study of the Spanish sample revealed that the minor allele (A) confers increased cancer risk at an early age. The analysis of the Dutch sample confirmed the association of the A allele, especially in homozygosity, with increased cancer risk in mutation carriers under the age of 45 (relative risk of homozygote AA = 2.90; 95% CI, 1.02-8.26). The SNP rs2075786 was not associated with colorectal cancer (CRC; 114500) risk in the general population or in non-Lynch CRC families. In silico studies predicted that the SNP causes the disruption of a transcription-binding site for a retinoid receptor, RXRA (180245), probably causing early telomerase activation and therefore accelerated carcinogenesis. Notably, cancer-affected Lynch syndrome patients with the AA genotype have shorter telomeres than those with GG. Bellido et al. (2013) concluded that MMR gene mutation carriers with the TERT rs2075786